During 1949–1962, a crystal-plasticity paradigm emerged that directly links microstructural dislocation activity to the macroscopic plastic response of polycrystalline aggregates. Research emphasized relating elastic behavior to plastic deformation via homogenization concepts, inter-grain constraints, and plastic potentials, enabling polycrystal yield criteria to be framed within a single, coherent framework. Methodological advances included modeling under combined stresses and integrating dislocation dynamics into continuum descriptions. Historical Significance: This period established the core of crystal-plasticity theory by tying elastic moduli to plastic properties and by highlighting dislocations as the principal carriers of plastic flow. Foundational ideas such as the plastic potential and the grain-scale constraints laid the groundwork for future crystal-plastic models and polycrystal yield predictions, influencing homogenization approaches for polycrystalline materials across disciplines.